The different types of communication signals are typically classified according to modulation type. Each of the various forms of modulation has its own set of advantages and disadvantages relative to a specific application for which it will be used. Some factors to consider in choosing a particular form of modulation include bandwidth, power consumption requirements, and the potential for signal propagation errors and recovery of the original information. For digital data, whether a separate clock signal is required or the modulated signal is self-clocking may be important. The relative simplicity or complexity of the modulating and demodulating equipment or circuitry may also be a factor in the decision. Low power consumption is particularly sought for use with capacitive-loaded transmission lines.
Each type of signal modulation has specialized decoder circuitry for performing the demodulation and data recovery. For example, for demodulation of a phase-modulated signal, U.S. Pat. No. 5,614,861 to Harada describes a system that employs a set of phase detectors with one input receiving the signal and at least one other input receiving a clock of specified phase delay. The results of the phase detection are input into data generation circuitry comprising logic gates for converting the detection results into a pair of data bits. In contrast, for demodulating a phase-shift-keyed signal, U.S. Pat. No. 6,204,726 to Toshinori includes a phase detector that compares an input signal against a divided master clock signal, the results of which are then logically processed, for example with a delaying circuit, subtractor, clock signal regenerator, phase compensator, adder and decision unit, to obtain a data bit for each keyed phase shift in the signal. A decoder circuit for a low power, high bandwidth, pulse width type of signal modulation would be desirable.